There is an increasing demand for image forming apparatuses employing electrophotographic technologies capable of printing full color images that are small, fast and affordable. Image forming apparatuses supply toner in small quantities each time printing is performed, and rapidly charge the supplied toner in order for continuous printing.
A compact sized image forming apparatus includes a proportionally compact sized developing device, and so the quantities of developer used by which may also be relatively small. Accordingly, the time between when toner is supplied and when toner is used for developing may be shortened.
In order to achieve a miniaturized high-speed developing device, electric charge to the toner should be provided at a higher charging rate. However, charging rates for color toner generally tend to be lower than that of black toner. If the charging rate is low, the toner may not be charged to a sufficient level, resulting in the toner particles being scattered. That is, when no toner scattering occurs if black toner is used, some toner scattering and resulting contamination of the internal components of the same developing device may still occur if color toner is being used.
Frictional electrification or triboelectric charging can be utilized to provide the electric charge to the toner. Frictional electrification however is susceptible to changes in the environment. In particular, if color toner is used, the amount of charge may vary considerably according to the changes in the environment, for example, a change in humidity. That is, for example, if the humidity is high, the charge imparted to the toner may be reduced, possibly resulting in toner particles scattering. When amount of toner charge changes, the print density may also change, which in turn may adversely impact the print quality.
Therefore, it is desirable to reduce the susceptibility of the charge amount of the toner to the environmental conditions, such as, e.g., humidity changes, particularly for a compact high-speed developing device.